The present invention relates generally to light sources used to illuminate body cavities during laparascopic surgery, and more particularly to a light assembly mounted in the distal end of an endoscope which emits white light, or red, blue, and green light within the body cavity during surgery.
Because of varying sizes and geometries, the interiors of various body cavities have different requirements for adequately illuminating them during the use of laparascopic (or endoscopic) cameras. An insufflated abdominal cavity, for example, has a volume of several liters, with the distance from the peritoneum to the liver bed ranging from 5 to 12 centimeters, depending upon the size and obesity of the patient. The geometry of the cavity is such that an angular field of view of between 50 to 80 degrees is desired for observation and illumination. Typical laparascopic surgical procedures necessitate endoscope-to-object distances of 1.5 to 15 centimeters.
Several illumination techniques are employed in the prior art. Where the endoscopic camera system uses white light illumination, a Xenon light source is typically focused onto one end of a flexible fiber optics cable. The other end of the cable is attached to a 90 degree coupling attached to an endoscope, the periphery of which comprises an annular fiber optics bundle terminating at the distal end of the endoscope. Light is emitted from the annular (donut shaped) fiber bundle into the body cavity where a portion of it is reflected and captured by the objective lens of the endoscope and relayed through the center of the scope to the CCD detector array. The white light thus must be separated, after the illumination step, into three primary components, usually red, green, and blue, before it can be processed into a color image by a non-sequential color CCD camera.
Field sequential cameras, on the other hand, utilize light sources which usually are separated into three primary colors prior to illumination of the object. Prior art sequential cameras, such as that described in U.S. Pat. No. 4,631,582 for example, utilize rotating segmented color filters in the path of white light sources, or color filters in the path of sequentially illuminated white strobe lights.
There are several problems associated with the prior art. Most light sources of the prior art are large, cumbersome, and inefficient. Thus, the efficiency of collection and transmission of light from a Xenon tube to the body cavity is poor, often as low as 0.1 percent. It is also difficult to match the angular spread of the light from the fiber optics cable to that of the angular field of view of the objective lens. Either the spread is too large, causing light to fall in areas where it is unusable, or the spread is smaller than the angular field of view of the objective, thereby causing vignetting. Additionally, the light distribution from prior art illumination sources is often a problem. A dark spot generally is located in the center of the picture causing the image quality to be inferior, particularly at close object distances. Also, the fiber optics cable used in prior art illumination devices comes into contact with the sterile zone in the operating room and thus must be re-sterilized before each use. The sterilization process often causes catastrophic damage to, or degrades, the cable. The present invention solves these and other problems characteristic of prior art laparascopic illumination systems.
An object of the present invention is to provide a system for illuminating body cavities during laparascopic surgery which is optically and energy efficient and which provides the desired angular dispersion of illuminating light.
Another object of the present invention is to eliminate the light-loss, size, and sterilization problems inherent in the use of fiber-optic cables and bundles.
Yet another object of the present invention is to adapt an illumination system for use with a field sequential single sensor video camera or with a sequential chrominance-luminance YC camera system.
In accordance with these and other objectives which will be apparent to those skilled in the art, the present invention comprises an efficient, compact, light source mounted in the distal end of an endoscope, usable with a field sequential single sensor video imaging system such as that described in co-pending U.S. patent application Ser. No. 905,278. A series of four red, fourteen green, and ten blue light emitting diodes (LED""s) are mounted and arranged on a ceramic substrate in a circular pattern concentrically around the optical path of the endoscope. A reflector cup surrounds each LED to help control the angular distribution of the emitted light. The LED""s are electrically wired to an illumination circuit which causes them to emit red, blue, and green light in synchronization with the field period of a CCD endoscopic camera. Because the LED""s are mounted in the distal end of the endoscope, the typical prior art light loss through fiber optics cables and connections is avoided and the need for cable sterilization is eliminated. The LED arrangement uniformly illuminates objects within body cavities with the required angular dispersion. The efficiency of the light source allows for battery operation of the camera and lights making the system much more portable.